Nightmare of a day. RCD tripiing under any load

brizospark · Aug 14, 2013

Have had one of them days. I had a board change to do and a few other bits and bobs so everything was going great until I tried to put power back on.

Basically I have replaced a 3036 board with a split load Wylex board. One half of the board is working fine but the other half's RCD is tripping as soon as anything is plugged into it.

If I remove all plugs from sockets then the RCD holds but as soon as I plug anything in, kettle, sky box, TV, it trips instantly. On this side of the board is the cooker, 1 x lighting circuit and 2 x ring mains, funny enough the RCD isn't tripping when the lighting circuit or cooker is on.

Now I have checked that I have neutrals from correct circuits going to the correct neutral bar, several times and these are OK. I tried replacing the RCD itself with the one that was OK and it still tripped. What else is strange is that the kitchen ring is on the side of the board which is fine but if I plug anything into a kitchen socket the RCD which isnt even protecting this is tripping!! I opened up sockets and everything looked OK but it was getting late on so I replaced the offending RCD with a main switch I had in van just so the couple have power on tonight before I go back again tomorrow. Switched on with RCD removed and everything fine.

Anyone had experience with this problem before? Any advice much appreciated

SJD · Aug 14, 2013

I'd also suggest neutral to earth fault somewhere, and not necessarily on the circuits on the problematic RCD.

sledgehammer · Aug 14, 2013

If its pme n-earth fault would common out both neutrals. I've had had exactly what you're talking about many times and its n-e.

wersolaruk · Aug 14, 2013

Could there be a borrowed neutral at that kitchen socket itself. Turn the rcd off covering that socket and turn other rcd on. Test between n-e at the problematic socket and if its showing voltage to earth it's a borrowed neutral! Sounds like a fault I would love to find!

Brightspark2 · Aug 14, 2013

sledgehammer said:
If its pme n-earth fault would common out both neutrals. I've had had exactly what you're talking about many times and its n-e.

Nice avatar :smartass2:....

brizospark · Aug 14, 2013

wersolaruk said:
Could there be a borrowed neutral at that kitchen socket itself. Turn the rcd off covering that socket and turn other rcd on. Test between n-e at the problematic socket and if its showing voltage to earth it's a borrowed neutral! Sounds like a fault I would love to find!

It's not just this kitchen socket it is any socket in house covered by either RCD

Richard Burns · Aug 14, 2013

brizospark said:
What's confusing me is why when I plug anything into kitchen socket covered by RCD A is it tripping RCD B? Surely this means it can't be a N to E fault as it would trip RCD B if this was the case

If you have an NE fault on a circuit on one RCD then loading a circuit on the other RCD can cause the first RCD to trip.
Did a diagram for you:

[ElectriciansForums.net] Nightmare of a day. RCD tripiing under any load

wersolaruk · Aug 14, 2013

You have a n-e fault, megger everything buddy! All fronts off etc, good luck with it mate!

shockboy · Aug 14, 2013

try lighting common fault landing light 2way neutral on upstairs circuit feed took from downstairs ciruit

markythesparky · Aug 14, 2013

brizospark said:
Thanks for replies guys yes everything tested out ok. So we are looking at a borrowed neutral most likely then?

If its a borrowed neutral then how did it test out ok?

bigspark17 · Aug 14, 2013

Borrowed neutral on light circuits.! Put all lights on same rcd and try.!

trev · Aug 14, 2013

bigspark17 said:
Borrowed neutral on light circuits.! Put all lights on same rcd and try.!

Or check to see if there really is one, locate it and eliminate it.

Engineer54 · Aug 15, 2013

Every time we get a thread about RCD's tripping after a CU change, the common consensus is either a N-E fault or a shared/borrowed neutral. And every single time the OP has failed to test the installation prior to replacing the old rewirable CU with one containing at least two RCD's.

How many more times do these guy's NEED to be told to test these installations before they start changing them out for god's sake??

What's more, why is this fault causing such a problem to find and rectify. I would have thought that in around an hour, an experienced electrician would have sorted this problem out, ...or at the very least well on his way to finishing off any remedial work...

markc123 · Aug 15, 2013

i=p/u said:
Test before touch

:shame: that's where i've been going wrong.

Wondered where my afro had come from.

brizospark · Aug 15, 2013

Eng54 do you honestly think in the real world customers would give the go ahead to carry out testing before changing a board? This would mean an additional cost on top of a board change The customer would simply get someone else to do the job!

trev · Aug 15, 2013

A test for borrowed neutrals plus an IR plus an EFLI wouldn't take very long at all would it?
You've already done enough there to identify any major problems and you're doing the rest of the tests anyway on completion of the change so what's the problem?